Philadelphia Federal Reserve Bank President Charles Plosser said that central bank purchases of mortgage-backed securities may be an inappropriate foray into policy that should be conducted by the U.S. Treasury.

“When the Fed engages in targeted credit programs that seek to alter the allocation of credit across markets, I believe it is engaging in fiscal policy and has breached the traditional boundaries established between the fiscal authorities and the central bank,” Plosser said according to prepared remarks of a speech he’s giving in New York today.

Federal Reserve Chairman Ben S. Bernanke and the Federal Open Market Committee are debating a new round of mortgage bond purchases to help boost the housing market and the economy.

“Central banks and monetary policy are not and cannot be real solutions to the unsustainable fiscal paths many countries currently face,” Plosser said on a panel at the University of Chicago’s Booth School of Business 2012 U.S. Monetary Policy Forum. “The only real answer rests with the fiscal authorities’ ability to develop credible commitments to sustainable fiscal paths.”